The present invention is directed to bicycles and, more particularly, to a bicycle sprocket apparatus that controls shifting of a chain from a smaller diameter sprocket to a larger diameter sprocket.
U.S. Pat. No. 4,889,521 discloses a multistage sprocket apparatus that includes at least one larger diameter sprocket and at least one smaller diameter sprocket assembled in a relationship such that the center point between a pair of adjacent teeth at the larger diameter sprocket and the center point between a pair of adjacent teeth at the smaller diameter sprocket are positioned on a tangent extending along the chain path when the chain is being shifted from the smaller diameter sprocket to the larger diameter sprocket. The distance between the center points is substantially equal to an integer multiple of the chain pitch. A chain guide portion is provided at the inside surface of the larger diameter sprocket at a position corresponding to the path of the chain when the chain travels between the center points for allowing the chain to move axially of the sprocket apparatus slightly toward the larger diameter sprocket. This facilitates shifting the chain from the smaller diameter sprocket to the larger diameter sprocket. One or more teeth on the larger diameter sprocket may be offset or inclined from a centerline of the sprocket body to further facilitate shifting the chain from the smaller diameter sprocket to the larger diameter sprocket. The system works so well that the chain usually firmly engages the teeth on the larger diameter sprocket even under severe pedaling pressure. However, engagement of the chain with the teeth of the larger diameter sprocket under such conditions may cause undesirable stresses on the chain and jolting to the rider.